I'm running 255/60/15 front and 275/60/15 rear with a 3.5/5 drop. The 275/60 is alot wider than a 235, so traction would improve. It's also and inch shorter than your current 235/75/15. If you like the tall tire that fills the fenders up, the 255/70/15 like PanelDeland mentioned would work better.
Here's a pic of mine.
